Electrically tunable full color display photonic crystals (PCs) made of a thin film of block copolymer, polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP), have been developed. The phase separation of PS and P2VP blocks leads to a one-dimensional periodic lamellar structure parallel to the surface of the thin film. In a solvent mixture of water and ethanol, each P2VP layer is swollen and partially charged. Applying a low voltage (<2.5 V) to such a thin film can lead to the repeatable expansion or contraction of each P2VP layer, depending on the direction and strength of the electrical potential. Such a variation of the lamellar periodicity leads to a full color display over a wide range from ultraviolet to near infrared. The advantages of such PCs are their facile preparation, low driving voltage and good durability, which make them potentially useful in information technologies.